Gearbox Software Support offers details on a patch for the PC edition of Aliens: Colonial Marines that's now automatically available through Steam. This offers a number of single-player and multiplayer bug-fixes, as outlined in this change list:

General

General user interface improvements.

Various performance improvements.

Fixed issue where a door may not function properly if a Xeno was killed while opening it.

Addressed issue where players could become stuck in a close encounter after killing a Lurker that had pounced them.

Fixed collision issue where bullets would not pass through certain open doorways.